Steel one-piece necked-in aerosol can

ABSTRACT

A one-piece, steel, aerosol can formed by a draw and iron process with varying wall thicknesses, including a main body of a first wall thickness, a cone area above of a greater second wall thickness and a curl area above of a third thickness smaller than the second thickness and adapted to fit a standard aerosol valve. A process for shaping the can with the respective wall thickness sections. The process includes necking the can near the top end. The bottom of the can may be supported to maintain a shape during necking. The can interior may be pressurized during necking to resist permanent deformation of the can during necking.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns a steel, one-piece, necked-in, aerosol can, which does not require a separate cone intermediate the wider top of the can body and the narrower outlet from the can or from a dispensing valve that is disposed in the outlet. It also concerns a method of manufacture of such a one piece can.

2. State of the Art

A typical two or three piece steel aerosol dispensing can has a selected diameter, which may be typically from 1½ inches (38 mm) to three inches (76 mm). Dispensing from an aerosol can is through a valve supported at the top of the can. The valve includes an attachment base, called a valve cup, by which it is attached to the can by crimping. The valve cup is narrower than the can body, e.g., a standard aerosol valve has about a one inch (25.4 mm) diameter. In order to support the valve at the top of the wider can body, a second can piece or dome (cone) is attached between the wide top of the can and the narrower valve cup. The dome has a wider bottom, having the diameter of the top end of the can body, and a narrower diameter top opening in which the valve cup is disposed. The bottom edge of the dome is shaped to mate with and be sealed to the top edge of the can in any of numerous conventional ways, but usually by seaming. However, the primary areas of possible leak or separation of the dome from a domed can is at the seam between the dome and the can body and a separate (in the case of a three piece can) seam between the bottom of the can and the can body. The top opening of the dome is sized to receive the valve cup and that opening also is defined by a small radius, inward or outward curl of the upper end of the dome. That curl provides a properly dimensioned seat for the valve cup and a gasket to seal against and strengthens the area where a connection is made to the valve cup, again conventionally, e.g. by crimping.

Alternately, the can body with an integral top with the opening to receive the valve may be made with an open bottom and a bottom closure may then be seamed on to complete the two piece can.

In the case of the separate seamed-on dome (or cone) or the integral body and top with an open bottom, the curl is formed with the aid of an internal mandrel or male die part to support the shoulder area of the dome or the integral top during the curl forming operation and thus prevents shoulder collapse. This mandrel cannot be used to support the shoulder during the necking and curl forming of a one-piece can since the bottom of the one-piece can is closed and will not allow insertion of the internal mandrel or male die part.

To avoid having to separately produce a dome (or bottom) and body (in the case of two piece cans) and a dome, cylindrical body and bottom (in the case of three piece cans), to save metal and energy, to simplify can assembly by avoiding the dome (and bottom) application step(s), to increase the pressure resistance of the crimped can, and to achieve a safer, more reliably sealed can, it would be desirable to form the can main body with an integral bottom and a selected diameter, yet have the body necked down in diameter to receive a valve or other closure at its reduced diameter opening at its upper end. This is commonly done by the method of impact extrusion followed by die or spin necking using pure aluminum or the more malleable alloys of aluminum although the resulting can is uneconomically thick with a high life-cycle energy cost. This may also be accomplished with certain aluminum alloys by forming a cylindrical body by the draw and iron, deep draw, or draw-thin-redraw method and subsequent die necking steps. To date, none of these methods has been successfully used to make a one-piece steel aerosol can, particularly in the diameter range of 38 mm to 76 mm.

When a cylindrical body of metal having a first thickness is necked down by the die necking process, the metal in the necked down region becomes progressively thicker as the diameter decreases. With many metals used for cans, such as steel, the necked down region also becomes work hardened during the necking step, and therefore more difficult to work and likely to crack when subsequently manipulated, as by being curled or attached, e.g. by crimping, to another part.

The undesired excess thickening effect is experienced with all metals and the work hardening effect is experienced with steel and some other metals, but excessive work hardening is typically not experienced with a softer metal, such as pure aluminum or its more malleable alloys. In these malleable, easy to work alloys, the thickening effect does not negatively impact the necking, curling and crimping operations. The upper end of a can of essentially pure aluminum or other soft, malleable metal can be necked down in diameter to reduce the size of an outlet opening to a selected smaller diameter without damage to the can or significant work hardening of the metal. Although steel 2-piece drawn and ironed food or beverage cans can be necked down to accept a conventional reduced diameter end (either plain or pop-top) of about 2 inch diameter, they have not been necked down to a diameter approaching the 1 inch diameter opening needed to fit a standard aerosol valve. Those steel cans that require an opening smaller than about 2 inch diameter are fitted with a separate end, cone or dome with the appropriate opening.

Heretofore, if an attempt was made to make a one piece steel aerosol can with a necked down region and a reduced sized opening, necking down the steel during the can forming process usually causes the steel to crack or buckle. When the curl area around the outlet from the necked down region is curled over or receives the valve cup and is crimped, it is likely to crack. Further, the metal in the necked down region becomes thickened, work hardened and thus less malleable.

Furthermore, eliminating a separate dome eliminates the steps of producing and of attaching the dome and also eliminates the additional material required for producing the dome and the scrap generated in the production of that dome. Thus, a one-piece can is inherently more environmentally friendly by virtue of its reduced use of source materials and the reduction in scrap.

SUMMARY OF THE INVENTION

According to the invention, a steel one-piece aerosol can body has varying wall thicknesses at different height regions along the can for serving respective purposes. Such a can can be made by a draw and iron process and can then be formed through necking and curling dies to form a one piece necked-in can with a larger diameter can body and a smaller diameter top opening. The region at and below the opening is called the neck. The top of the can body defines an area called the shoulder, at which the can body begins necking in. Between the narrow neck and the wide shoulder there is a narrowing frustoconical shape region called the cone.

The region of the neck at the opening into the can can then be curled to accept a standard aerosol valve cup. The can has a sloping “cone” shape joining the shoulder of the body and the neck. This “cone” may be of any one of a number of appropriate shapes including spherical, oval, conical, tapered, stepped, etc. The body of the can may be formed into any one of a number of non-cylindrical shapes for aesthetic or ergonomic purposes.

The invention particularly concerns selection of can wall thicknesses of a preferably one piece, preferably steel can according to the purpose each region of the can body, namely, the bottom, side wall, shoulder, cone, neck and curl area performs, how the can is formed and particularly necked to receive a valve cup at its opening and the characteristics of the metal, preferably steel, of the can body. In particular, in a one-piece steel can, the curl area above the shoulder and the cone is made appropriately thin prior to necking so that when it is thickened by being necked in, the curl area is then capable of being worked into a curl without damage to the can body or shoulder. Further, the cone area must be thick enough to not collapse when it is necked in, typically by a die element applying force to the shoulder in the axial direction or by a spinning device with a roller assist. Also, the valve, which is supported by its valve cup on the curl area, has a base piece which is shaped and sized to be crimped against and form a seal with the inside of the shoulder. The cone area above the shoulder must be thick and strong enough to resist buckling under the axial loads generated during necking, curling and crimping and also to maintain the seal formed during the crimping.

In a typical can according to the invention, before the can is necked, the can wall at the curl area is thinner than the can wall at the cone area below the curl area. Even after necking in, which thickens the curl area proportionally more than the cone area, the curl area remains thinner than the cone area.

In addition, the cone area of the necked-in can, between the narrowed neck and the can body, should be sufficiently strong to resist collapse of the neck of the can due to axial loads applied to the can during its forming. This is accomplished by providing a sufficient thickness of metal in the cone area between the main can body and the narrowed neck or curl area. In the case of the softer metals, such as aluminum, the axial load required to form the cone and neck is much lower than that required for forming the cone and neck of a steel can. The present invention permits a valve cup to be attached to steel cans of various diameters.

As the can diameter increases, the thickness of the cone area is preferably adjusted due to the force required to neck in from the wider diameter shoulder, to avoid collapse of the cone.

To make the curling operation easier, to reduce the axial loads generated during curling, and to eliminate cracking and cone area collapse, the portion of the upper can wall above the cone area and that will become the curl area can be thinned to a thickness other than the thickness of the cone area beneath the curl area so that after necking the curl area, is of a thickness that is optimal for curling.

The wall of the main body of the can below the shoulder may be made of a thickness suitable for the type of service, e.g., the diameter of the can and the pressure in the can, required of the can. The thickness of the body wall is typically not dependent upon the thickness of the bottom, the cone area or the curl area of the can. The thickness of the cone area can be made sufficiently thick to resist buckling under the axial loads generated during the necking and curling operations. The thickness of the curl area can be chosen to optimize the forming of the curl, and so that it has strength to retain its shape and hold the valve cup. In fact, in some prior cans, the flange area above the cone, which is seamed or crimped to a dome, is thicker walled than the cone area. The foregoing thicknesses are achieved by choosing the appropriate thickness of sheet or coil stock from which the can is made and providing an ironing punch of the appropriate configuration to produce the required wall thickness distribution along the length of the can as discussed above.

The thickness of the can bottom is chosen to provide the strength or pressure resistance required to maintain the shape of the can bottom of a filled, fully pressurized can. For enhanced strength resistance to deformation when a can is pressurized, the can bottom may be domed upward, into the can. That strengthened shape is preferably produced, or, if present, maintained when the can is being necked. It is desirable that the can bottom also be of a thickness substantially of the can wall. However, such a can bottom may be too weak to maintain the original shape it had prior to necking the can, because necking involves applying downward force on the can and the can bottom. To maintain the desired shape of the can bottom during necking, it may be supported on a die or mandrel with a selected shape, so that the can bottom should not collapse or be deformed from its desired shape. Of course, the same die may be used to provide a preferred shape to the can bottom so that the bottom is given its selected shape when the can is being necked.

When a can is of a sufficiently large size, and its can wall material is strong enough and the wall is thick enough to support a filled can shape during normal product storage and use, the can wall and possibly the can bottom may not be sufficiently strong to resist being deformed by the axially or vertically directed force applied to the can body during the necking process. Rather than changing one of the above parameters of the can to increase its strength, an elevated pressure condition may be temporarily produced inside the can being necked, either by application of air pressure or by hydraulic pressure supplied by a source of hydraulic pressure. Residue of hydraulic pressurizing fluid can be removed in the customary can washing step. The pressure level is selected so as to not significantly or permanently deform the can, but to be sufficient to aid in preventing can deformation or collapse under the axial force applied during necking.

The present invention deals with steel one-piece aerosol cans with reductions at the necked-in (curl) region, for example, of about 33% for 38 mm diameter cans, about 44% for 45 mm cans, about 52% for 53 mm cans, about 56% for 58 mm cans, and about 61% for 65 mm cans (if economics and/or technical considerations justify the one piece 65 mm cans).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section of a fragment of a can showing a formed but un-necked can wall,

FIG. 2 is a cross-section of a fragment of a can showing a necked can wall.

FIG. 3 shows the can of FIG. 2 completed with a valve.

FIG. 4 shows a supported can bottom to maintain shape and schematically illustrates application of pressure in the can body during necking.

DESCRIPTION OF A PREFERRED EMBODIMENT

An aerosol can 10 is formed from a steel blank or a steel cup using a drawn and ironing process.

As shown in drawing FIG. 1, the side wall 12 of the lower region of the can 10, below the shoulder 17, is cylindrical and of a substantially uniform first thickness 13, thick enough to contain a fluid material and propellant under pressure in the can and for the diameter of the can, yet the wall is economically thin enough. The closed bottom 15 of the can is usually thicker than the first thickness, and may be domed inward to strengthen it against deformation, e.g., from pressure in the can. The thickness of the can bottom is preferably low to keep the can of light weight and to reduce the amount of metal used. During below described necking of the can, the illustrated dome shape may be supported by a die or mandrel.

As shown in FIG. 2, the can is necked narrower upward in a “cone” shape from the condition shown in FIG. 1 at its upper region starting upward from the shoulder 17. That cone area 14 should be strong enough to resist cone area collapse when axial loads are applied to the can during the necking, curling, and crimping processes. Therefore, the cone area 14 of the side wall of the can is made with a greater second wall thickness 16 than the first thickness 13. The top of the lower region 12 meets the bottom of the cone area at the shoulder 17, where the cone area 14 starts its slope inward.

Directly above the sloping cone area 14 is the neck or curl area 18, which is curled outward on a small radius to define a support area for a conventional aerosol valve 20 to be crimped into the can thus sealing the valve to the can. See FIG. 3. The valve includes a valve cup 34 shown crimped at the base 32 of the valve cup allowing a seal for the can contents to be formed at 36. The peripheral edge region 38 of the valve cup is curled over to receive the curl area 18.

The third wall thickness 19 of the curl area 18 before necking is thinner than the second wall thickness 16 of the cone area 14. The curl area may be either thicker or thinner than the first wall thickness 13 of the side wall of the lower region of the can, because these sections have different purposes, as was described above. The curl area 18 is necked down to the maximum extent in defining the outlet opening 21 which receives the valve cup 34 or some other closure for the can opening. The necking thickens the curl area from the thickness 19 in FIG. 1 to the greater thickness 23 in FIG. 2, but not so much as to make the curl area unbendable and uncurlable. The curl area 18 above the cone area is still thin enough and malleable enough as to be curlable to define the curled peripheral region 18 around the top opening 21.

The cone area 14 of the can wall is thickened as at 16 so that it will not buckle or collapse under the axially downwardly directed necking force applied during can forming and also during later application of the valve to the finished can. Since the upper section of the cone area at 22 and the curl area 18 thicken at 26 and 23 respectively during the necking process, the curl area starts thinner at 19 in FIG. 1 so that the thickness 23 of the necked down and thickened curl area in FIG. 2 is sufficiently thin to reduce the chance of the metal cracking there when it is bent to form the curl. The can wall at the cone area has a maximum second thickness just below the curl area and just below where at 24 the curl area 18 is joined to the top of the cone area 14. This maximum wall thickness is selected to resist shoulder collapse due to axial loads encountered during forming.

As described above, the bottom 15 of the can may be supported by a die or mandrel 31 that maintains a selected shape, e.g., a dome shape, under axial force applied by a conventional necking device 27 in the plane of the can wall. For a can of a relatively larger cross-section or diameter, elevated pressure is temporarily supplied in the can during necking, e.g., by air pressure or hydraulic pressure at 29, which helps the entire can body resist permanent deformation under the force of necking the can.

When the curl area 18 is necked in, the cone area 14 deflects above the shoulder to slope inwardly as well. The cone area is thick enough at thickness 26, so that it does not buckle, but instead the can wall slopes inward generally in the region between the top of the can body and the cone area below where the shoulder thickens.

In an example for illustrating the invention, in a steel aerosol can having a diameter of 1¾″ (45 mm), before necking of the can, the first thickness 13 of the body wall is 0.0044″ (0.112 mm), the second thickness 16 of the cone area is 0.0065″ (0.165 mm) and the third thickness 19 of the curl area is 0.005″ (0.127 mm). After the can is necked, the thickness of the material of the cone area increase in the direction toward the narrowed neck, and the thickness of the curl or neck area increases, possibly to greater than 0.0062″ (0.127 mm), but remains thinner than the thickness in the adjacent cone area. Note that the first thickness of the body wall is independent of the second and third thicknesses of the cone and curl areas as is the thickness of the bottom.

To neck the top of the can, the punch of a draw and iron die (not shown) is shaped to provide the thicker wall at the cone area 14 and the thinner wall at the curl area 18. It is already known to provide a punch in a draw and iron die to have a shape to change the thickness of the top of a two-piece can to provide a thicker, stronger area for the formation of a flange for seaming on an end, dome or cone. But a punch shaped for providing a thicker wall at the shoulder area and a thinner wall at the curl area is not known. The punch in the draw and iron die is a direct complement to the shape of the can wall being initially formed before the can is necked. As described above during necking, the can bottom may be supported to maintain its shape and the interior of the can may be pressurized to resist and prevent permanent deformation of the can body during the necking.

Alternatively, a conventional technique may be used for necking the can, including using conventional shaping dies, or a spinning device with a roller assist, coupled with ultrasonic vibration which warms the can material and helps reorient it without applying too much force.

Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims. 

What is claimed is:
 1. A steel can adapted for necking and adapted for use as an aerosol can, the can comprising: a can body comprised of a can wall; a lower region of the can wall having a first thickness and being of a first diameter; a cone area of the can wall above the lower region, and the cone area having a second wall thickness; a curl area of the can wall above the cone area, the curl area having a thinner third thickness than the second thickness of the cone area, wherein the second and third thicknesses are selected for enabling necking of the can wall at the cone area and the curl area and for enabling forming a curl of the can wall at the curl area after the necking.
 2. The can of claim 1, wherein the third thickness of the can wall at the curl area is different than the first thickness of the lower region of the can body.
 3. The can of claim 2, wherein the second thickness is different than the first thickness.
 4. The can of claim 1, wherein the can body has a closed bottom and an open top having the curl area at the top, and the can wall is necked to a smaller second diameter opening at the curl area.
 5. The can of claim 4, wherein the can body and bottom are integral.
 6. The can of claim 4, wherein the can body and bottom are of one piece.
 7. The can of claim 1, wherein the can body is of one piece.
 8. The can of claim 7, wherein the can body is formed by a draw and iron process.
 9. The can of claim 1, wherein the can is an aerosol can.
 10. The can of claim 1, wherein the can has an opening and the can further comprising an aerosol dispensing valve secured into the opening of the can at a base of the curl area.
 11. A process for forming a one-piece steel can with a narrow opening, the method comprising forming a can body having a can wall with a lower region of a first wall thickness, a cone area of the can wall above the lower region with a second wall thickness and a curl area of the can wall above the cone area with a third thickness smaller than the second thickness, the curl area surrounding and defining an opening into the can body; necking the can by applying force to the can for reducing the diameter of the can at the curl area to a smaller diameter than the diameter of the lower region and forming the can body in the cone area to define the smaller diameter for the curl area for shaping the opening for receiving an aerosol valve after necking and curling.
 12. The method of claim 11, wherein the can body is formed in a draw and iron process.
 13. The method of claim 11, further comprising forming the second thickness to be different than the first thickness.
 14. The method of claim 13, further comprising forming the third thickness to be different than the first thickness.
 15. The method of claim 11, further comprising forming the third thickness to be different than the first thickness.
 16. The method of claim 11, further comprising installing an aerosol valve in the opening at the curl area.
 17. The method of claim 11, wherein the can body has a can bottom below the lower region of the can wall; the method further comprising supporting the can bottom on a shaped die or mandrel which resists deformation of the can bottom during can necking.
 18. The method of claim 11, further comprising applying pressure inside the can body during the step of necking to assist the can body in resisting permanent deformation during the can necking. 